Referring to FIGS. 1 to 3, a plastic binding element 10, as disclosed in U.S. Pat. No. 2,910,068, includes a back plate 11, a plurality of middle fingers 12 and two outer end fingers 13 extending from a long side 111 of the back plate 11, and two T-shaped slots 14 formed in the back plate 11 proximate to the other long side 112 thereof. The middle fingers 12 can be curled to form closed rings. Each outer end finger 13 has a tapered end portion 15 which is notched as at 17 to form a neck 16 in close proximity to the tapered end portion 15. Each T-shaped slot 14 has a base portion 141 and a top portion 142. The base portion 141 has a width slightly greater than the neck 16. The top portion 142 has a width slightly greater than that of each outer end finger 13. The outer end fingers 13 can be curled to form closed rings and inserted into the top portions 142 of the respective T-shaped slots 14. When the neck 16 of each outer end finger 13 enters the base portion 141 of the respective T-shaped slot 14, each outer end finger 13 and the backplate 11 are interlocked. Since the greatest stress is on the outer end fingers 13, the outer end fingers 13 are mechanically interlocked with the back plate 11.
Although the aforesaid plastic binding element 10 can achieve its intended purpose, it has the following drawbacks:
1. The papers 20 to be bound must have binding holes 21 corresponding to the middle fingers 12 and the outer end fingers 13, so that the middle fingers 12 and the outer end fingers 13 can be inserted one by one into the binding holes 21 to thereby bind the papers 20. However, different sizes of papers to be bound usually have different number of binding holes, so that the plastic binding element 10 is not applicable for use in different sizes of papers to be bound.
2. When the papers 20 to be bound do not have binding holes, the user must first use a puncher to punch binding holes 21 into the papers 20 so as to correspond in number to the middle fingers 12 and the outer end fingers 13 of the plastic binding element 10, after which the plastic binding element 10 is used to bind the papers 20. However, if small sized papers 20 are to be bound and only have a few binding holes, the plastic binding element 10 is also not applicable in this case.